Typically, the major constituent parts of these devices, such as the bodies, blades, and shafts, are made of suitable metals, and the shafts are often journaled on the bodies by means of metal bearings, such as ball bearing races. The main bore through the body is finished to proper diameter. The blade is either machined or stamped, and then must be individually adjusted on the shaft at assembly to secure proper fit.
In order to co-jointly attain desired throttling characteristics and assure consistently proper functionality, it is necessary for the bore and blade geometry and construction to be exact, rigid and dimensionally stable. At engine idle, the blade-to-bore clearance must be quite small, a typical radial gap between blade and bore having an area equivalent to a hole of about 0.10 inch diameter. Heretofore, it has been typical design practice to make the throttle blade of non-circular shape, one prevalent shape being elliptical. Production tolerances must be closely controlled, and the impact of thermal, chemical, and/or mechanical interactions that may be encountered in service must be minimized. Accordingly, significant costs are associated with the production of throttle bodies of automotive internal combustion engines, and this is an area where meaningful cost savings can be attained with innovative technology.
The present invention represents new technology that can provide improvements and meaningful cost savings through novel throttle blade constructions. A throttle blade embodying principles of the invention can be manufactured in a circular shape in such a way that it can attain the same or better throttling and functional characteristics possessed by prior non-circular blades without incurring many of the expenses that are associated with the manufacture, assembly, and adjustment of the prior blades.
Stated briefly and in a somewhat generic way, a throttle blade according to one aspect of the invention comprises a rigid main blade body that can be either metal or composite (plastic) and that contains a resilient seal around at least a majority of its outer margin, the radially outermost portion of the seal lying on a circle whose diameter is essentially equal to that of the circular throttle body bore within which the throttle blade is disposed in the throttle body assembly. Several embodiments of seals will be described.
One of these embodiments is an elastomeric seal that is insert-molded onto the outer margin of the main blade body, and another aspect of the invention involves the method of making this embodiment of blade.
Moreover, the use of an elastomeric seal allows the throttle body to be fabricated by molding of a composite material so that machining of the throttle bore is unnecessary. Fabrication of the main blade body by the molding of composite allows the blade and shaft to be assembled together in an expedient manner, and also gives rise to an expedient way to fabricate the shaft.
A circular shape for the radially outermost part of the blade, coupled with resiliency thereof, is more tolerant of the normal dimensional variations that occur in the mass production of throttle body assemblies. Moreover, the effect of friction between the blade and the wall of the throttle bore becomes less significant because primary contact between the two will occur at smaller radii from the shaft as viewed along the shaft axis.